justyo

Yo (justyo.co) was a single-tap notification app and "the world's simplest API." A service registered an API username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python, PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical Yo API surface for the record.

justyo publishes 2 APIs on the APIs.io network: Account API and Yo API. Tagged areas include Company, Notification, Push Notifications, Messaging, and Mobile.

justyo’s developer surface includes documentation, signup flow, authentication, and 13 more developer resources.

🌐 Visit website 📡 Source on GitHub
0.0/100 minimal Agent 0/100 human only saas Full breakdown ↓
scored 2026-09-25 · rubric v0.23.0
1 APIs
CompanyNotificationPush NotificationsMessagingMobileDeveloper ToolsDefunct

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-09-25 · rubric v0.23.0
Composite quality — 0.0/100 · minimal
Contract Quality 0.0 / 19
Developer Ergonomics 0.0 / 15
Access Clarity 0.0 / 15
Operational Transparency 0.0 / 10
Contract Governance 0.0 / 9
Discoverability 0.0 / 8
Regulatory Posture 1.8 / 15
Create-or-Update Ergonomics 0.0 / 10
Agent readiness — 0/100 · human only
Machine-Readable Contract 18 / 18
Agentic Access Contract 0 / 10
Documented Reversibility 0 / 6
MCP Server 0 / 12
Machine-Readable Auth 10 / 10
Idempotency 0 / 9
Stable Error Semantics 8 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 7 / 7
Typed Event Surface 0 / 6
Agent Skills 5 / 5
Well-Known Catalog 0 / 4
Consent & Bot Identity 0 / 3
A2A Agent Card 0 / 8
Dry-Run / Simulate Mode 0 / 4
Delegated User Identity 0 / 6
Protected Resource Metadata 0 / 5
Registration Without a Human 0 / 6
Agentic Commerce Well-Known Document 0 / 5
Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.
Create-or-Update Ergonomics applies to this provider. This API accepts writes, so it carries 10 points of the composite. It is scored from the published contracts themselves: whether a caller can create-or-update in one call, whether the write accepts a key the caller already holds, and whether the response says which branch ran. Without that, every write needs a search-and-branch in front of it, and the first time that check is skipped a duplicate record is created. Scored against the observed mean rather than raw — a provider at the catalog average is unchanged by this facet, not penalised by it.
The six quality facets above are damped to 75 points between them, because the conditional facet above carries the other 25. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 75% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.
Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from github.com/api-evangelist/justyo: open an issue to ask a question, or submit a pull request to add artifacts. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

APIs 2

Individual APIs this provider publishes, each with its own machine-readable definition.

justyo Account API

Read account/subscriber information.

justyo Yo API

Send Yo notifications to subscribers.

Open Collections 3

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

API Collection

OPEN COLLECTION

Yo Account API

OPEN COLLECTION

Account Yo API

OPEN COLLECTION

Rate Limits 1

Documented rate limits and quota policies.

Justyo Rate Limits

1 limits

RATE LIMITS

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Justyo Authentication

apiKey · 1 scheme

SECURITY

Justyo Domain Security

no transport/DNS hardening detected

SECURITY

Resources

Get Started 2

Portal, sign-up, and the first successful call

DeveloperPortal
DeveloperPortal
 SignUp
SignUp

Documentation 1

Reference material describing how the API behaves

Documentation
Documentation

Agent Surfaces 4

MCP servers, agent skills, and machine-readable catalogs

X-MCPServerCandidate
X-MCPServerCandidate
 LLMsTxt
LLMsTxt
 WellKnown
WellKnown
 AgentSkill
AgentSkill

Design & Contract 2

Pagination, idempotency, versioning, errors, and events

Conventions
Conventions
 Lifecycle
Lifecycle

Build 3

SDKs, sample code, and the tooling you integrate with

GitHubOrganization
GitHubOrganization
 Packages
Packages
 SDKs
SDKs

Access & Security 2

Authentication, authorization, and security posture

Authentication
Authentication
 DomainSecurity
DomainSecurity

Company 1

The organization behind the API

Website
Website

Other 1

Properties that don't map to a standard resource type

Overlay
Overlay

Source (apis.yml)

apis.yml Raw ↑ 
aid: justyo
name: justyo
description: 'Yo (justyo.co) was a single-tap notification app and "the world''s simplest API." A service registered an API
  username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all
  subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push
  — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python,
  PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co
  host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical
  Yo API surface for the record.'
url: https://raw.githubusercontent.com/api-evangelist/justyo/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- slow-ventures
x-tier: stub
x-tier-reason: portfolio-lead
x-status: defunct
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: false
  label: Hosted service · you call their endpoint
  confidence: medium
  source:
  - openapi
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - rate-limits
  - security
  generated: '2026-09-03'
  method: derived
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-09-16'
image: https://raw.githubusercontent.com/api-evangelist/justyo/refs/heads/main/openapi/justyo-yo-openapi.yml
tags:
- Company
- Notification
- Push Notifications
- Messaging
- Mobile
- Developer Tools
- Defunct
tags_raw:
- Company
- Notifications
- Push Notifications
- Messaging
- Mobile
- Developer Tools
- API
- Defunct
apis:
- aid: justyo:justyo-account-api
  name: justyo Account API
  description: Read account/subscriber information.
  humanURL: https://docs.justyo.co/
  baseURL: https://api.justyo.co
  tags:
  - Account
  properties:
  - type: OpenAPI
    url: openapi/justyo-account-api-openapi.yml
  - type: Authentication
    url: authentication/justyo-authentication.yml
  - type: RateLimits
    url: rate-limits/justyo-rate-limits.yml
  - type: ErrorCatalog
    url: errors/justyo-problem-types.yml
  - type: DataModel
    url: data-model/justyo-data-model.yml
  - type: Conventions
    url: conventions/justyo-conventions.yml
- aid: justyo:justyo-yo-api
  name: justyo Yo API
  description: Send Yo notifications to subscribers.
  humanURL: https://docs.justyo.co/
  baseURL: https://api.justyo.co
  tags:
  - Yo
  properties:
  - type: OpenAPI
    url: openapi/justyo-yo-api-openapi.yml
  - type: Authentication
    url: authentication/justyo-authentication.yml
  - type: RateLimits
    url: rate-limits/justyo-rate-limits.yml
  - type: ErrorCatalog
    url: errors/justyo-problem-types.yml
  - type: DataModel
    url: data-model/justyo-data-model.yml
  - type: Conventions
    url: conventions/justyo-conventions.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: Overlay
  url: overlays/justyo-yo-overlay.yaml
- type: Website
  url: https://justyo.co
- type: Documentation
  url: https://docs.justyo.co/
- type: DeveloperPortal
  url: http://dev.justyo.co/
- type: GitHubOrganization
  url: https://github.com/YoApp
- type: SignUp
  url: https://dashboard.justyo.co/
- type: Packages
  url: packages/justyo-packages.yml
- type: SDKs
  url: packages/justyo-packages.yml
- type: X-MCPServerCandidate
  url: mcp/justyo-mcp.yml
  note: 'Renamed from MCPServer 2026-09-03 (roadmap#247): the manifest self-describes as status: candidate — a tool list derived
    from the published API contracts, not an existing server. The scorer already read the manifest and reported mcp_server
    correctly; the MCPServer type was crediting the artifact-type surfaces with a server that does not exist.'
- type: LLMsTxt
  url: llms/justyo-llms.txt
- type: WellKnown
  url: well-known/justyo-well-known.yml
- type: Authentication
  url: authentication/justyo-authentication.yml
- type: Conventions
  url: conventions/justyo-conventions.yml
- type: Lifecycle
  url: lifecycle/justyo-lifecycle.yml
- type: DomainSecurity
  url: security/justyo-domain-security.yml
- type: AgentSkill
  url: skills/_index.yml
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence

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